Some electronic devices use a haptic actuator to provide a haptic output to a user. The haptic output can notify the user of an incoming message, a telephone call, an upcoming event, and so on. The haptic output may include a vibration or movement that is perceived by the user.
In some cases, the haptic actuator is a linear actuator that includes a moveable mass. The moveable mass may be driven at various frequencies to provide different kinds of haptic output. For example, an electromotive force may be applied to the moveable mass which causes the moveable mass to move from a first position to a second position and back again. However, when the moveable mass is driven at regular intervals, the moveable mass may begin to exhibit unwanted movement. For example, the moveable mass may begin to excite a higher order resonance mode which causes the moveable mass to rotate about an axis, rock back and forth in a seesaw type motion, and so on. When the moveable mass moves in such a manner, the moveable mass may impact or otherwise collide with a housing of the haptic actuator thereby causing undesirable noises and possible damage to the electronic device or the haptic actuator.